There has been a large response to a research paper published in Environmental Science and Technology by Avner Vengosh at Duke and a group of researchers, including ones in Jordan (Omar Rimawi, Abdallah Zoubi and Emad Akkawi at Al Balqa Applied University). The paper reports a finding of very high concentrations of the natural isotopes of radium in the water of the Disi Aquifer in the south of the country.
From a psychological perspective, the news is very bad, as it combines peoples’ extreme fear of all things radioactive with a concern that the long awaited savior (the Disi conduit) may never be implemented. But, what do the findings mean and what don’t they mean?
The ministry of water and irrigation put out a statement denying that there are abnormal amounts of radiation in the water used for drinking. It is important to note the difference between having high total radiation and having high concentrations of radium. The confusion caused by the name of the isotope should not be used to change the subject. The total radioactivity may be low, but at the same time individual isotopes may be higher than standards set as limits for them by regulators.
Radium falls in the second column of the periodic table, making it an alkali earth, like calcium. As such, it may be absorbed into calcium-bearing tissue in the body (mostly bone), which means that it would pose a danger as an internal radiation source at high enough concentrations. Radium is also worrisome because it emits alpha particles, which cause the most damage when absorbed internally.
But how are “high enough” concentrations determined? There are various ways to determine this. Some claim that there is no such thing as a “safe exposure level”. If this is the case, then everybody is in trouble, because we are all exposed to various types of ionizing radiation all the time. The average human being is exposed to about 300 millirems per year, which varies according to latitude, altitude and geology of where he/she lives. It is impossible to get away from this minimal exposure no matter what a person does.
Researchers use different approaches at determining “safe exposure limits”. In my opinion, the most satisfying is the use of epidemiological data, where a large population living under certain conditions is compared statistically with the general population. Based on such data, US standards for combined 226Ra and 228Ra in drinking water is 5 pCi (picocuries) per liter. This works out to 73 mrem after an exposure of 30 years.
Setting standards is not an exact science, and in the case of radiation, exposure limits are typically set along the ALARA (as low as reasonably achievable) principle. Beyond that, linking the disease with an environmental factor by plotting the amount of exposure and the number of cancer cases on a scatter diagram. If there is a link between exposure and cancer increases, a correlation can be seen between increasing exposure and increasing cancer rates. Typically, the correlation is very distinct at high exposures and less so at low exposures. At some point, when cancer incidence reaches background levels, the relationship between exposure and cancer incidence becomes questionable.
In the case of radium, studies of exposure are extensive and have been summarized in book published by Argone National Laboratories in the US under the title “Radium in Humans: A review of US studies” (available here). This book well illustrates how epidemiological studies work. It describes exposures to dial paint workers, people who drank radium spiked water for “medicinal” purposes as well as people who lived in areas with high radium water supplies. The conclusion (on page 112) is that a threshold can be set at 1000 cGy (equivalent to 10 Grey or 1000 rad). This is echoed in page 2 of the book, which states that “No symptoms from internal radium have been recognized at levels lower than those associated with radium-induced malignancy. Radium levels 1,000 times the natural 226Ra levels found in all individuals apparently do little or no recognizable damage. These statements may suggest that a threshold exists for radium-induced malignancies; at least, they recognize that the available data demonstrate a steep dose response, with the risk dropping very rapidly for lower radium doses”.
Thus, it is no surprise to read cases like the town in Illinois that had to set up an expensive radium removal facility to remedy its high radium waters, only to see the EPA change the drinking water standard by a factor of 10, which would have made the facility pointless. The EPA seems to have kept the old standard, but it is illustrative that a good case could have been made to set the standards at 50 pCi instead of 5 pCi.
So, how does the Disi water stack up? According to the published paper, 226Ra concentrations range from 0.1 to 1.13 Bq/l (2.7 to 30.5 pCi/l), with a median of about 0.9 Bq/l (24.3 pCi). For 228Ra, the concentrations range from 0.12 to 2.14 Bq/l (3.2 to 37.8 pCi/l). The waters thus range from meeting the EPA standards to those reaching 20 times the said standards.
Thus, in dealing with questions related to radium content in the water of the Disi aquifer, three points need to be made. The first is that the science and data used to formulate the standards needs to be critically evaluated, as the standards may be too stringent and the benefits derived from removing the radium from the water may be questionable. The second point is that the water from the various sources of the aquifer will be mixed together and with those from other sources, and so the water reaching the consumer will have lower radium contents, depending on the mixing ratios and the contents of the different sources. The third point is that radium can be removed from the water if epidemiological data justifies the cost of doing so.